The robust bonding of plastic materials is useful in the manufacture of many devices. Many devices, for example, medical devices, can have challenging bond requirements in terms of strength, durability, flexure, and permeability. It has been a particular challenge to satisfy applications involving bonding of elastomers, which are conventionally defined as polymeric materials able to be elongated at least 100% without experiencing yield or other failure. In many instances the difficulty lies in forming a bond that has the strength, flexibility, and integrity of the material adjacent to the bonded area. In addition, it is important to provide a bonded area that exhibits resistance to fatigue and polymer fracture failure. Because of this, bonded elastomers in which the bonded area is the same as the components being bonded can outperform alternative bonding methods.
Elastomeric polymers can be bonded with adhesives. However, it can be difficult to identify an adhesive that provides a strong bond between components formed of elastomeric materials. Typical adhesives capable of bonding elastomeric polymers with sufficient strength often fail to form a lasting bond because the mechanical properties of the adhesives generally do not match the mechanical properties of the elastomeric components which they join.
In an alternative approach, elastomeric components can be bonded by application of conductive heat and pressure to the region to be bonded. Such bonding is commonly achieved by holding together the components to be bonded and pressing them between heated platens. The platens are typically metallic, and it is therefore difficult or impossible to monitor the position of the components or the completeness of the bond during bonding. Defects are common and difficult to avoid. Moreover, due to manufacturing requirements, there are often long periods during which the platens must be held at high temperature, but are not being actively used for bonding. This can consume considerable energy and can pose burn risks for personnel operating the bonding equipment.
Components formed of thermosetting polymers such as synthetic rubber can be bonded by placing uncured polymer material between the components and then vulcanizing the uncured polymer material. In many cases this vulcanization bonding process entails the use of heated platens and thus entails the difficulties outlined above. Moreover, where the composition of the uncured polymer material is not identical to that of the components being bonded, the dissimilarity in mechanical properties can lead to failure of the bond.
Ultrasound and RF bonding can be used to join polymeric components. However, like heat sealing and vulcanization bonding, these bonding methods generally employ opaque, metal platens that interfere with observation of the alignment and layout of the components during bonding.
Ultrasonic welding can be used to bond polymeric components. To be effective, the ultrasonic waves must be transmitted through a rigid plastic material to an energy director zone in contact with another rigid plastic material. Energy dissipation occurs through conversion of the ultrasound vibrational energy to heat at the interface, where bonding occurs.
Friction or spin bonding is sometimes used to bond polymeric components, but these techniques are not suitable where static positioning of the components is required for considerations such as proper fit, alignment, and orientation of the components.
Staking and similar attachment methods using fastening devices such as screws, bolts, rivets and the like generally do not provide hermetic seals without the addition of gasket materials which require frames, brackets or similar support, defeating the intent of bonding without the use of additional extraneous material. Moreover, the use of additional materials to either form or seal the joint can lead to failure arising from the dissimilar mechanical properties of the materials used.